Structural rehabilitation represents an important aspect of the construction industry and its significance is increasing. Strengthening is the process of increasing of the existing capacity of a non-damaged structure or a structural component to a specified level. The main aim of this work is to compare the strengthening techniques by bonded and unbounded mechanical connection as well as studying of replacing internal tension bars by external steel plate with the traditional method of bonding by glues on ultimate strength of RC beams. The traditional method use the epoxy glues for interfaces bonding while the idea of these techniques is a connection of external steel plate with RC beams by shear connectors mechanically. The experimental work involves flexural testing of six concrete beams of 100 150 1500mm. The test variable includes the percentage of replacing the internal reinforcement with external steel plate. Comparison of methods of bonded and unbounded beam is implemented with the method of strengthening by glue. Results show that beams reinforced with external steel plate behave as a composite action right up to ultimate load and the mode of failure occurs by yielding of external plate, pullout or yielding the shear connectors not by separation of plate. Using of external steel plate restrains central deflection in the beam with increasing of load capacity by increasing thickness of plates.